Hydatid cyst is a zoonotic disease and endemic in Turkey. The disease can involve any organ. The most common involved organ is lung in childhood. Hydatid cyst of lung may be asymptomatic or may be sometimes ruptured or infected. Secondary bacterial infections associated with the hydatid cyst are well known. A previously not reported pediatric case of hydatid cyst with Mycoplasma pneumoniae pneumonia is described in this report. It is emphasized that M. pneumoniae should be kept in mind as a cause of infected hydatid cyst which is unresponsive to beta-laktam antibiotics...